Switch



May l, 1934.

A. VISCHER, JR., ET AL SWITCH 2 sheets-sheet 1 Filed Dec. 27, 1932 INVENToRs 7;/ ATTORNEY A. VISCHER, JR., E T AL 1 SWITCH Filed Deo. 27, v1932 May 1; 1934.

2 Sheets-Sheet 2 I YK "65' S f m Flags.

' ATTORNEY v Patented May 1, 1934 UNITED STATES PATENT F'FICE swrrcn Application December 27, 1932, Serial No. 648,878

11 Claims.

This invention relates to snap switches and particularly to thermostatically actuated electric switches adapted for a variety of purposes. One application of the improved thermostatic switches of the present invention is illustrated in the pending application of Herbert L. Paulding, Serial No.

603,468, filed April 6, 1932. However, such switches may be used formany purposes other than those illustrated, particularly whenever it is desired to provide remote control of the operlations of devices by means of electrical impulses.

The bimetallic thermostat of the present invention may be used, if desired, to control the actuation of devices not of anelectrical nature.

In the accompanying drawings Fig. l is a plan view of one form ofthermostatic switch constructed in accordance with the present invention, with the cover member in horizontal section, and with the external electric circuits conventionally illus- 'trated; Fig. 2 is a vertical longitudinal section through the device along the line 2 2 of Fig. l; Fig. 3 is a vertical transverse section on line 3 3 of Fig. 2; Fig. 4 is a vertical transverse section on line 4 4 of Fig. 2; Fig. 5 is a plan view, similar Ato Fig. 1, of a modified form of thermostatic switch; Fig. 6 is a side elevation of the device of Fig. 5, with the cover member in vertical longitudinal section; Fig. 7 is a vertical transverse section on line 7 7 of Fig. 6; Fig. 8 is a horizontal `section on line 8 8 of Fig. 6; Fig. 9 is a vertical transverse section on line 9 9 of Fig. 8; Fig. 10 is a diagrammatic view of the circuits involved in the embodiment of Figures 5-9.

The thermostatic switch of the present invention is designed to act with a positive snap action, and with a relatively small throw, requiring only slight variations in temperature to operate the switch. This is important in devices, such'as the present, in which the heat required to operate the switch is to be generated Within the instrument itself, at the will of an operator, and in a relatively short time, that is, in a. few seconds or even less. To this end, the heat responsive element l1 is made up of two bimetallic strips, 12 and 13, welded or otherwise joined togethc? at their adjacent ends, as at 14. In the construction illustrated, in connection with this form of the invention, the high expansion sides of the two strips, which are convex at all temperatures, are joined together, forming a reverse curved or S-shaped heat-responsive element l1. If desired the low expansion sides may be joined in lieu of the high expansion side. This in the present case would have the advantage of permitting two similar metals to be welded together.

(Cl. 20o-122) The metals used in the preferred embodiment of the heat responsive element in this form of the invention are a special steel, such as a nickelchrome, austenitic steel with a high coeicient of expansion, and invar in the one strip 12, and a copper alloy, such as a bronze containing, say, 90 copper, with a similar high coefficient of expansion, and invar in the other strip 13. This particular combination is chosen for a purpose hereinafter disclosed. However, the novelty and utility of the present device do not depend upon the particular materials used, and any suitable metals having varying coeflicients of expansion and other-properties to be mentioned hereinafter, may be used.

The element 11 is carried, under suitable compression stress, between the grooved lug 15, formed upon the upper end of contact post 16, and the grooved insulation member 17, carried by the lug 18, which is formed upon the upper end of contact post 19. The contact posts l6 and 19, as well as contact posts 20 and 2l, hereinafter referred to, and the cover bracket 22, are all mounted upon any suitable base 23, preferably formed of insulating material.

The bimetallic strip 13 is pierced by a contact member 24, which projects slightly on both sides of the strip. The movement of the heat responsive element l1 and the contact member 24 carried by strip 13 thereof is restricted between the insulated stop member 25 and the contact point 26, both of which are'adjustable in a transverse direction. The bimetallic strip 12 is provided with a heating coil 27, which is wound over a layer of insulation 28 wrapped or otherwise applied around a section of the strip. The ne wire leads 29 and 30 of the coil 27 are soldered or otherwise secured to the rigid conductors 31 and 32, respectively, which are in turn connected in any suitable manner with the contact posts 19 and 20. The contact point 26 is adjustably mounted in the upwardly extending bifurcated portion of binding post 2l, while the insulated stop member 25 is similarly mounted on binding post 20.

The contact point 26 is adjusted to such a position that the point of contraflexure of the element 11 will always be on the side of the axis of compression next the insulated stop 25, except when the device is operated as hereinafter described. That is, the element 11 is, normally, in such a position that the compressive stress exerted at its endsi'tends to force its central portion away from contact point 26, and toward the insulated stop 25. Furthermore, the arrangement of the two strips 12 and 13 is such that if they are both heated uniformly, or to the saine extent, as by the action of the sun beating down upon the cabinet in which the .switch is housed, they have a mutually compensating eiect and the element 11 will not snap.

However, when the steel and invar strip 12 is heated by the passage of a current or" electricity through the coil 27, the unequal expansion of the two metam causes the strip 12 to decrease its radius of curvature, which results in the movement of the point of contraiiexure of the element 11 to a position on the other side of the axis of compression, causing the element 11 to snap toward the contact point 26. 'I'he contact member 24 is thus brought against contact point 26.

If the current through coil 27 is now interrupted the heat generated will quickly be equalized throughout element l1, and will cause an expansion of the copper alloy side of strip 13 which will again shift the point of contraexure of element ll to its former position, causing element 11 to snap back to its normal position, and breaking the contact between contact member 24 and contact point 26. This action is aided by the use of a copper alloy instead of steel in strip 13, since copper is a much better conductor of heat than steel, and aids in the speedy conduction of heat to all parts of strip 13 and hence in the more rapid dissipation of the heat.

The circuit which is closed by the contact between the members 24 and 26 may be, as shown in the present embodiment, a battery circuit for energizing an annunciator, although it will be clear that it may be for other purposes and may draw vits electrical energy from any suitable source. This circuit is connected into the thermostatic switch by means of the contact posts 16 and 21.

The heating circuit may draw its energy from any suitable source of supply, such as the battery illustrated. The energizing of the heating circuit, in the present embodiment, is accomplished by the action of a sensitive relay, illustrated conventionally at 33, which in turn may be energized by a slight current impulse originating at a distant point. The particular control employed forms no part of the present invention, and any suitable means may be used for energizing the heating circuit. It may, for example, be directly controlled by a make and break device located at a remote point. The thermostatic switch, in the arrangement shown serves in the capacity of a relay controlling the current flow through the strip 13.

In the embodiment illustrated in Figs. 5-9, inclusive, a somewhat different arrangement is employed for a different purpose. In this form of our invention the contact between the contact member 24a and the contact point 26a is intended, when once established, to be maintained. in-

' definitely or for considerable periods, the heat energy necessary to this end being derived from a circuit energized through the action of a relay or other device operated, for instance, by the current impulses employed in the sending of signals, such as telegraphic messages and the like. However, the particular source of the initial operating impulses is not a feature of the present invention, and we do not Wish to be limited in that respect.

In the present form of switch, the heat responsive element 11a is made up of two bimetallic strips 12a and 13a, joined in the same manner as in the iirst form hereinbefore described. These strips, in the present embodiment, are preierably of like metals, steel and invar being used in each strip, and' the ends of the strips are joined with their like faces together. Other suitable metals may be substituted.

The heat responsive element 11a is mounted in the same manner as the member 11 hereinbefore described, While the contact point 26a is mounted in the same way as point 26. In place of the insulated stop member 25 of the rst embodiment, a contact point 34 is provided, against which the contact member 24a is adapted normally to rest. Two heating coils, 35 and 36, are carried by the bimetallic strip 12a, these being secured thereto in any suitable manner, as by the wire clamp 37. Each of the coils 35 and 36 is wound upon a core consisting preferably of a copper strip, the coils being separated from these strips by layers of material providing electrical insulation. The ends of each copper core are bent back upon themselves to form a complete loop. Coil 35, as shown, is mounted on but insulated from one branch of a copper core 38 of the character mentioned, while the coil 36 is mounted on, but insulated from a branch of a copper core 39. A strip of copper 40, in the shape of an inverted U is inserted in the loops formed by the cores 38 and 39, one leg of the U being embraced Within each loop. Insulating material separates the U-member 40 from the current conductors of the coils 35 and 36. In this manner the coils are joined together in such a way that the heat generated by either coil will be transmitted, through the copper cores and U-member 40, to the bimetallic strip 12a.

The coils 35 and 36 are of dierent electrical resistance, for instance, coil 36 may be of 1000 ohms resistance and coil 35 of 5000 ohms. By the arrangement of circuits which will be presently described, the coil 35 will be in parallel with a much smaller or negligible resistance, which may conveniently be the motor or other load to be thrown in upon operation of the switch, upon the initial operation of the make and break device or relay 33a, so that the resistance of the circuit at this time will be substantially limited to that of coil 36. When the heat responsive element 11a, due to the heating eiect of the current through coil 36, changes its position, bringing the contact member 24a against contact point 26a, the coil 35 is placeddirectly in series with coil 36 and the low resistance shunt around the coil 35 is eliminated. This greatly increases the resistance oi.' the heating circuit, and reduces the Vheating eiect, causing the generation of just enough heat to maintain the heat responsive element 11a in its new position. At the same time, the making of contact between 24a and 26a more or less permanently closes a circuit through the motor or other load, 41, placing the latter in parallel with the heating coils. This load circuit will remain closed until the relay 33a has been cie-energized for a suflicient period to allow the heat responsive element 11a to cool oiI to a certain extent and return to its normalposition.

The arrangement of circuits tov effect the foregoing results, best shown in Fig. 10, is as follows: A battery 42, or other suitable source of current, is connected to contact posts 43 and 44. From the conductor joining the battery 42 and the contact post 44, a branch is provided through the relay 33a. to contact post 45, which is connected by suitable means to one end of coil 36.Y From the conductor joining the battery 42 and the contact post 43 a branch is provided, which extends through the motor 41 to contact post 46, thence through the bitmetallic strip 13a to Contact ber 24a. Coil 35 is connected between contact post 43 and contact point 34. vCoil 36 is con-a nected between contact post 45 and contact point 34.. The bi-metallic strip, it will be understood,

compared with that of the coil 35, most of the current will pass through the motor and the result will be substantially the same as though the coil 35 were not in the circuit. After the heat responsive element lla is actuated, two circuits, in parallel, are established, one of which includes the motor 4l and the other of which includes coils 35 and 36 directly in series. Whenever the relay 33a is de-energizedthe latter circuit is opened but the motor circuit will remain continuously closed.. While the motor 41 is in the initial heating circuit, the resistance of this circuit is so great due to the inclusion of coil 36, and the current, accordingly, so small, that the motor remains at rest during the initial heating period. After throwing of the contact 24a to the Contact 26a in the initial period, the motor circuit will remain closed with no outside resistance so long as relay 33a is suiciently energized to keep the coils 35 and 36 heated.v If desired the circuits may be modied somewhat to completely eliminate the coil 35 from the circuit during the initial heating period in lieu of simply shunting the major portion of the current around this coil. However, the arrangement shown has the advantage of simplicity.

The terms employed in the foregoing description are terms of description and not of limitation, and we do not wish to be limited t'o the particular constructions illustrated and described,

as many modications of the same may be made without departing from the scope of our invention.

` What we claim is:

1. In a thermostatic switch, a heat responsive element comprising two bimetallic strips joined at their adjacent ends to form an S-curve, the high-expansion sides of the s'aid strips being at all times convex. y

2. In a thermostatic switch, a heat responsive element comprising two bimetallic stripsjoined at their adjacent ends to form an S- curve having' the high expansion sides of the strips at all times convex, and a resistance coil wound upon one of said strips.

3. In a .thermostatic switch, a heat responsive element comprising two connected bimetallic strips, one of said strips being formed of metals of relatively low thermal conductivity, the other of said strips including a metal of relatively high thermal conductivity.

4. In a thermostatic switch, ahe'at responsive element comprising two connected bimetallic strips, one of said strips being formed of metals of relatively low thermal conductivity, the other of said strips including a metal of relatively high thermal conductivity, and means for heating the first mentioned strip.

5. In a thermostatic switch, a heat responsive element comprising two connected bimetallic strips, one of said strips being formed of steel and invar, and the other bf said strips being formed of copper alloy and invar.

6. In a thermostatic switch, a heat responsive element and a plurality of electrically energized heating coils associated therewith, 'said-coils being connected in series, a pair of fixed contacts, a contact carried by said element shiftable from one of said Xed contacts to the otherupon energization of said coils, one of said contacts being arranged to shunt a low resistance across one of said coils while said element is in normal position, said shunt being eliminated and said coils connected directly inseries by the shifting of the ,ducting relation to said element, and means associated with said contacts for varying the current ow through said coils upon shifting of said element.

l8. In a snap switchla spring element, means Y for confining said element to produce an S-curve.

said means retaining said element with its ends curved constantly in the same directions, means for varying the radius of curvature of the ends of said element, a iixed contact, and a contact carried by said element at a point nearer one end of the element than the other and adapted to be engaged with and disengaged from said fixed contact upon variation of the radius of curvature of the ends of said element.

9. In a device of the class described, a bimetallic heat responsive lelement tensioned to provide a snap action between two positions, a pairv of contacts, only one of said contacts being engaged by said element in each position, and a plurality of heating coils carried by sa'id element, said coils being arranged in series and having their connected ends joined with one of said contacts.

l0. In a device of the class described, a bime- .tallic heat responsive element tensioned to provide a snap action between two positions, a pair of contacts, only one of said contacts being engaged by said element in each position, a plu'- rality of heating coils carried by said element, said coils being arranged in series and having their connected ends joined with one of said contacts, and means for connecting the other of said contacts and the free ends of said coils into electric circuits.

11. In a device of the class described, a bimetallic heat responsive element tensioned to provide a snap action between two positions, a pair of contacts, only one of said contacts being engaged by said element in each position, a `plurality of heating coils carried by said element, said coils being arranged in series and having their connected ends joined with one of said contacts, and means for connecting the other of said contacts, the free ends of said coils, and one end of said element into Aelectrical circuits.

ALFRED VISCHER, JR. HERBERT L. PAULDING. 

